ARM: S5P: Fix the platform external interrupt issues.

This patch does the following:

1. Corrects the common platform code for external interrupts for using the
   VIC mask/unmask bits also.
2. Moves the common defines related to external interrupt for plat-s5p
   to common files.
3. Based on the new common defines, corresponding changes are made in the
   affected platforms (S5P6440, S5P6442 and S5PC100).

Signed-off-by: Pannaga Bhushan <p.bhushan@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>